The invention relates to a process for resistance welding of metal parts in accordance with the preamble of claim 1.
1. Technical Field
The invention in particular relates to a resistance welding process for welding together metal parts, at least one of which has a soiled or roughened surface.
For resistance welding, the metal parts to be welded together customarily are arranged overlapping each other and clamped between two welding electrodes. In the course of the welding process, one of the welding electrodes is trackingly guided in accordance with the deformation of the welded parts in order to assure the clamped seating. An electrical voltage is applied to the welding electrodes for welding the metal parts together, so that an electrical current flows through the welding electrodes and through the metal parts. Because of the relatively high contact resistance between the metal parts to be welded, the areas of the metal parts through which current flows are strongly heated by the current flow and are welded together. This type of resistance welding, which is usually employed, results in an insufficient welding quality when welding metal parts with soiled or roughened surfaces together.
2. Representation of the Invention
It is the object of the invention to make available a process for resistance welding of metal parts, which results in a satisfactory welding quality even in connection with the welding of metal parts with soiled or roughened surfaces.
In accordance with the invention, this object is attained by means of the characterizing features of claim 1. Particularly advantageous embodiments of the invention are described in the dependent claims.
To perform the resistance welding process in accordance with the invention, the metal parts to be welded together are arranged overlapping each other between a first and a second welding electrode. The metal parts to be welded together are moreover clampingly fixed in place between the welding electrodes. In accordance with the invention, at least one of the two welding electrodes is embodied as a circular cylinder, which is seated so it rotates around its cylinder axis, and rests with its surface area against one of the metal parts. A sliding friction is generated, at least during the time in which the welding electrodes and the metal parts are charged with the welding current, between the surface area of the circular cylinder and the metal part on which it rests by rotating the at least one welding electrode embodied as a circular cylinder. The surface of the metal part resting against the circular cylinder and facing the surface area is cleaned and/or smoothed in the area of the weld during the actual welding process by the friction, and the electrical contact between the at least one welding electrode embodied as a circular cylinder, and the metal part resting against it is improved by this. Furthermore, the rotation in accordance with the invention of the at least one welding electrode embodied as a circular cylinder prevents the occurrence of the so-called adhesive effect between the welding electrode and the metal part to be welded. The term adhesive effect describes an adhesion of a welding electrode to the metal part with which it is in contact during the welding process. The adhesion of the welding electrodes and the metal part is severed again by pulling the welding electrodes apart following the termination of the welding process. However, this can lead to damage to the welding electrode or the welded connection.
Advantageously at least one welding electrode embodied as a circular cylinder is already caused to rotate prior to the actual welding process. Moreover, the rubbed-off material caused by the sliding friction and adhering to the surface area of the at least one welding electrode embodied as a circular cylinder is cleaned off, preferably with the aid of a cleaning device. The cleaning process advantageously already takes place during the welding process in order to assure a uniform welding quality. Possible damages to the surface of the welding electrodes, which had been caused by the transition of the welding current in the area of the weld, are removed by the cleaning process.
The resistance welding process in accordance with the invention can be applied particularly advantageously for welding together foil-like or sheet-like metal parts with soiled or roughened surfaces and wire-like or rod-like metal parts.